R1:d02256df3ca5

Remove very old "vsDiff" data from commit update / diff extraction pipeline

Summary:
Ref T13276. This was introduced in D2586 to power a "trigger audits when the committed change does not match the reviewed change" feature. It was removed without ceremony in D15939. Broadly, rebases mean that this sort of feature can't really work like this and this approach is inherently unreliable; see also T182.

This property no longer has readers, and is unlikely to get any in the future since my planned pathway for…